The objective of this study is to characterize the effects of phencyclidine on identified neurons in the central nervous system of laboratory animals in order to elucidate its mechanism of action. The current year's project was to identify its action on central noradrenergic pathways. Many of the studies were carried out in anesthetized rats, in which a noradrenergic pathway from the pontine nucleus locus coeruleus to the cerebellar Purkinje neuron has been demonstrated anatomically and physiologically. Local administration of norepinephrine to Purkinje neurons by microiontophoresis or pressure ejection through a multibarreled micropipette causes an inhibition of spontaneous discharge which we monitor by extracellular single neuron recording. Phencyclidine mimics these depressant effects of norepinephrine in normal animals. Like those of norepinephrine, these effects of phencyclidine can be blocked by neuroleptic drugs or lithium carbonate.